In a clear attack on the Labour leadership’s track record, he added: "When it comes to the particular, they are prepared to indulge in sentiment that is profoundly antisemitic."
Speaking in front of former Labour frontbench colleagues Ed Balls and Yvette Cooper, Mr Blair added: "Antisemitism is today back in a way I never considered conceivable or possible.
"I want you to know - which is why I'm so pleased that Ed and Yvette are here, along with so many other Labour members of parliament too - that for those of us who know what the Labour Party should really be about there is nothing more abhorrent than the notion that antisemitism is alive in the party today."
He added: "When people talk about Jewish finances, some of the criticisms of George Soros, statements about Trumps supporting Jews and the statement, I'm afraid as ignorant as it was unpleasant, suggesting that a section of British Jewry doesn't understand a British sense of irony – when, by the way, anyone familiar with Jewish humour knows that the Jewish community has turned irony into virtually an art form."
The former PM suggested singling out the state of Israel for criticism above other nations was another form of antisemitism.
He said that Israel was still the sole democracy in the Middle East and praised its free media, its rule of law and the fact that it staged the only Gay Pride event in the region.
But Mr Blair added that "no fiercer critics of the government of Israel are to be found than in the state of Israel."
He suggested that "Zionism as conceived by Hertzl is a homeland for the Jewish people”, but he added that "Zionists are not people who do not want see health and justice for the Palestinians."
Striking a note of optimism as he finished his speech, Mr Blair paid tribute to the Holocaust survivors present at the event and said: "What we are fighting is not just something that happened in history; this is something profoundly relevant which will decide the future for us.
"What side are we on: the side of progress or prejudice?
"This is the challenge - and I am optimistic about this
"We are never going to forget and we are never going to give up -and in the end we will win."
Education Secretary Damian Hinds also spoke and pledged government funding for a further three years for HET"S "Lessons From Auschwitz" project, which last year took more than 3,000 students and teachers from schools across the UK on a four-part course including a one-day visit to Auschwitz-Birkenenau.
Mr Hinds said he hoped the announcement would bring "stability and clarity" to the project.
Home Secretary Sajid Javid was the final political speaker to be introduced by compere Emma Barnett, the BBC radio and TV presenter.
Mr Javid praised his bus driver father's role in helping him understand and grow to love Israel and also spoke of the need to fully understand the tragedy of the Holocaust.
Earlier Karen Pollock, HET's chief executive, warned the audience - including Labour MPs Luciana Berger, Louise Ellman, Ruth Smeeth and Wes Streeting, along with Conservative Friends of Israel chair Stephen Crabb - of the threat from the rise of the far-right across Europe.
But she also hit out at Mr Corbyn's party over its failure to "recognise antisemtism."
Susan Pollack - the survivor who lost 50 members of her family in the Shoah - also delivered a moving address to the audience, which also included ITV's Judge Robert Rinder and Natasha Kaplinsky.
